Reaction injection molding (RIM) has become an important process for the production of external automotive body parts and other types of molded products. The process entails the precise metering of two streams of highly reactive liquid components, direct impingement and the intimate mixing of the two streams at high pressure, non-turbulent flow of the mixed components into a closed mold at atmospheric pressure and the completion of the chemical reaction within the mold itself. One of the streams comprises a polyisocyanate component and the second stream includes a isocyanate-reactive component. The polyisocyanate component is typically based on a liquid polyisocyanate. The isocyanate-reactive component contains a high molecular weight component, typically a polyol and/or an amine polyether, and usually also contains a chain extender having amino and/or hydroxyl groups. U.S. Pat. No. 4,218,543 describes a current commercial RIM process.
A modification of the RIM process is the Reinforced Reaction Injection Molding (RRIM) process whereby a reinforcing agent is introduced into the system. Typically, the reinforcing agent comprises glass fibers which impart to the molded article superior mechanical properties. Parts reinforced with glass flakes having a nominal size of about 1/64" offer isotropy and a good profile of mechanical and physical properties. Among the disadvantages associated with these parts is their low DOI values. These values which characterize the surface quality of a painted part may be determined in accordance with a test method known as General Motors Method GM 9101-P which utilizes a lighted "glow box". Alternatively, these values may be determined by an ATI apparatus which is a digital DOI meter.
Spherical particles are not effective in improving the mechanical properties of parts made by RRIM while the use of fiberous or platy fillers contributes to a considerable improvement in the level of the physical properties. Generally, the improved mechanical properties are associated with flake or fiber reinforcement which have an aspect ratio (defined as the ratio between the length of the fiber to its diameter or the ratio of the largest lateral dimension of the flake to its thickness) which is greater than 20. Commonly, glass fibers and flake reinforcement used in the context of RRIM have aspect ratios in the range of 50 to about 150.
The prior art is noted to include the articles "Mica as a Reinforcement For Polyurethane RIM", by Saurabh Naik et al in Plastics Compounding, May/June 1986, pp. 16-21, and in "Development of R-RIM Urethane for Automotive Exterior Parts", by Nishikawa et al, Jap. Plast. Age Vol. 24, Iss 209, pp. 17-23, May-June 1986, both of which disclosed mica as a filler in these applications. In an article entitled "Impact Properties of Reinforced RIM Fascia" by Rice et al (Journal of Cellular plastics March/April 1983, pp. 114), there is disclosed relevant technology. Mica has been mentioned as having a size of 200 mesh. In "Reaction Injection Molding of Mica Reinforced Polyurethane" by Remillard et al in Polymer Composites, October 1986 Vol. 7, No. 5 pp. 395, there is disclosed relevant technology entailing a particular grade of mica. Also relevant is the article entitled "High Modulus RIM Elastomers For Automobile Exterior Body Panels" by Metzger et al in Journal of Cellular Plastics, September/October 1981, pp. 268. In "Variables in reinforced RIM" by McBrayer in Elastomeric, July 1980, there is disclosed mica said to be of a high aspect ratio. In "Reinforced polyurethanes for Car Body Parts" in Kunststoff, (1981) 9, pp. 577-584, Seel et al disclose mica in a relevant material system and conclude that the material characteristics are solely dependent on the concentration of the mica and that they are largely independent of the diameter of the platelets. The diameter of the platelets is said to have an effect on the levels of elongation at break, tensile strength and impact resistance. These are said to be better with platelets having smaller diameters. While mica has been previously mentioned as a filler or as a reinforcing agent in several relevant systems--see for instance U.S. Pat. Nos. 4,525,491, 4,530,941 and 4,524,044--there is no evidence that the mica entailed in the present invention which combines fine particle size and high aspect ratio was used in the past or that its use in the system of the present invention was suggested.
It is an object of the invention to provide a reinforcement for a RIM material system which would yield to the resulting molded part a good combination of mechanical properties and DOI values.
It is a further object of the invention to provide an improvement to the RRIM process which would result in the production of molded parts having desirable properties including both mechanical and esthetic properties.